In the production of oil and gas a well bore is formed which extends downwardly from the earth's surface. The well bore is formed by cutting into the earth's surface with a rotary bit attached to a drill string formed from joints of pipe sequentially attached as the well bore is extended downwardly. A drilling mud is circulated through the hollow drill string, jetted through and across the face of the drill bit, and then passed upwardly through the well bore as the well is drilled. Eventually, at some predetermined depth, the drill string is tripped out of the surface hole, a casing string is run and cemented in place and drilling is resumed until a producing stratum is reached which tests show is economically feasible for completion of the well. Casing is set, a production tubing constituted of couplings and interconnected sections of pipe, or joints of pipe, is run downwardly from the earth's surface to the producing stratum, the well is brought in, and oil and gas flow from the producing stratum through the production tubing to the earth's surface.
The average depth to which oil and gas wells are drilled increases from year to year, as does the hostility of the environment in which the wells are set. Bottom hole temperatures and pressures are quite high, and increase with increasing depths. The acidity, and corrosiveness of this environment is one to which production tubing is constantly exposed and must continuously function in delivering oil and gas to the earth's surface.
In U.S. Pat. No. 2,980,451, which issued Apr. 18, 1961 to William B. Taylor and Wilbur H. Griffin, there is described an improvement in sealing production tubing which has admirably served the oil and gas industry for many years. The couplings and interconnected sections of pipe, or joints of pipe, which constitute the Taylor-Griffin production tubing are provided with seals in the couplings and joints which prevent leakage in wells where enormous pressures are encountered. The seals are formed within the coupling members, and joints, by providing lateral circumferential flat bottomed, straight side walled grooves which are cut within a threaded inside wall of the coupling members, and joints, within which are mounted seal rings, or packing rings constituted of a generally non-resilient extrudable material. The externally threaded male members, when the coupling members, and joints, are made up, compress, deform and extrude to some extent the rings within their retaining grooves to form an effective leak-proof seal. However, albeit production tubing formed by the coupling members, and joints, in such manner have been effectively sealed, the seals have contributed to the corrosiveness of production tubing. Examination and study of production tubing sealed in this manner has shown considerable corrosion on the outside walls of the coupling members, and joints, opposite the sealing areas.